Residual feed intake (RFI) is an alternative measurement of feed efficiency, which is theoretically independent of production level and body size, calculated as the difference between actual feed intake and predicted DMI based on metabolic BW and ADG. The objective of this work was to identify the relationships between RFI and size of important internal organs in Nellore bulls classified in low and high RFI levels. Thirty three young Nellore bulls, with minimum RFI -0.640 and maximum RFI 0.690, were slaughtered and had their internal organs weighted. Table bellow shows the least-square means of final BW (FBW); empty BW (EBW); liver (LIV); kidney (KID); gastrointestinal tract (GIT); KPH; and other internal organs (IOR). No differences were detected in body size between low and high RFI bulls. Low RFI bulls had smaller important internal organs (LIV, KID, and GIT) than high RFI bulls. For KPH, no differences were detected. Low RFI bulls ate less than high RFI bulls, had smaller internal organs and the same fat content.

Table 1. Internal organs of low and high RFI bulls

LOW RFI

(n=18)

HIGH RFI

(n=15)

P

FBW, kg

374a

391a

0.1148

EBW, kg

343a

357a

0.1797

LIV, kg

4.16b

4.63a

0.0043

KID, g

673b

786a

0.0389

GIT, kg

21.8b

24.3a

0.0411

KPH, kg

5.25a

5.38a

0.8018

IOR, kg

10.4a

11.1a

0.0711

Within a row, means with a common superscript letter do not differ (P < 0.05) by least-square means adjusted for Pdiff.